The present invention relates generally to mufflers for modifying the sound produced by the exhaust from internal combustion engines. More specifically, the present invention relates to mufflers that produce a desired resonance accompanied by enhanced engine performance.
Various laws have mandated the use of exhaust mufflers with internal combustion engines in order to meet sound attenuation standards on public roadways. High performance engines used in vehicles such as sports cars are generally designed to provide peak power at higher engine speeds. Unfortunately, the conventional exhaust muffler systems used in a vehicle having a high performance engine can produce undesirably high back pressure, thereby limiting top end speed and performance of the vehicle.
Typically, original equipment muffler manufacturers for vehicles, such as sports cars, have been only marginally concerned with this limiting of performance (i.e., horsepower drop) which occurs as a result of the muffler""s sound attenuation. Accordingly, owners of high performance automobiles, such as sports cars, have relied on after-market muffler manufacturers to provide higher performance mufflers for their cars, while meeting the legal sound attenuation requirements.
Beyond simply meeting the legal sound attenuation requirements, the owners of high performance sports cars have long sought exhaust mufflers that produce a deep, throaty, xe2x80x9csports carxe2x80x9d exhaust sound. That being stated, an exhaust muffler for use in a sports car that produces any high frequency resonance, buzzing, or raspy exhaust sound is highly undesirable because it is irritating to the driver.
Consequently, for many years there have been after-market muffler assemblies available which produce a throaty sports car exhaust sound, while maintaining the sound within legal noise limits and while providing at least somewhat enhanced engine performance. One such after-market muffler has been produced in many similar versions generally known as xe2x80x9cglasspackxe2x80x9d mufflers. These mufflers employ an elongated tubular casing having a layer of fiberglass material around the inner periphery of the casing. The fiberglass is retained in place in the casing by a perforate tubular shell mounted inside the casing. Various gas-directing partitions or baffle structures is have been used inside the fiberglass retaining shell to assist in dispersing gases and sound for attenuation.
Glasspack mufflers may initially produce the desired throaty sports car sound, but with time, the high gas temperature and exhaust gas velocity break down and erode away the fiberglass. This problem is exacerbated by cars which have catalytic converters because the exhaust gas output from a catalytic converter and reaching the muffler is much hotter than the exhaust gas input into the catalytic converter.
Thermal erosion of fiberglass has been addressed by substituting a ceramic fiber blanket as a sound absorption material in mufflers. While this approach has been suitable to address the thermal breakdown problems caused by the heat of the exhaust gas as it passes through the muffler, the high velocity of the exhaust gas still erodes the ceramic blankets.
The use of partitions in glasspack mufflers to attenuate sound has also been accompanied by undesirable side effects. In particular, the partitions tend to increase back pressure by choking flow through the muffler, thus decreasing engine performance. In addition, the partitions may also increase exhaust gas velocity proximate the fiberglass, thus increasing the rate of fiberglass erosion and breakdown. Furthermore, glasspack mufflers also have a tendency to rap, or make a cracking sound, during acceleration and deceleration caused by sound waves that are not allowed to expand. This sound is highly undesirable to the sports car enthusiast.
Thus, what is needed is an exhaust muffler that is inexpensive, durable under attack of hot and corrosive exhaust gas, and readily adaptable as an after-market replacement for the original equipment mufflers installed in high performance vehicles. Moreover, what is needed is an exhaust muffler that provides efficient noise attenuation while not causing undue back pressure to the engine or undue noise harmonics that are irritating to the driver. That is, an exhaust muffler is needed that provides a throaty sports car sound without degrading engine performance.
Accordingly, it is an advantage of the present invention that an exhaust muffler for an internal combustion engine is provided.
It is another advantage of the present invention that an exhaust muffler is provided that produces a deep, throaty sound.
It is another advantage of the present invention that a desired resonance is provided without causing undue back pressure to the engine.
It is another advantage of the present invention that the exhaust muffler produces a desired resonance without irritating noise harmonics.
Yet another advantage of the present invention is that an exhaust muffler is provided that is durable, cost effective, and readily adaptable to a number of vehicular exhaust system configurations.
The above and other advantages of the present invention are carried out in one form by an exhaust muffler for an internal combustion engine. The exhaust muffler includes a curved inner tube. The curved inner tube includes a first leg having a first perforate region and a first imperforate region arranged about a circumference of the first leg and a second leg having a second perforate region and a second imperforate region arranged about a circumference of the second leg. The second leg is aligned with the first leg so that the second imperforate region faces the first imperforate region on an inside curve of the curved inner tube. A curved portion of the curved inner tube interconnects the first and second legs. An exhaust inlet is in communication with a first end of the first leg and is configured to receive exhaust gases from the engine. An exhaust outlet is in communication with a second end of the second leg and is configured to output the exhaust gases. A muffler housing encloses the curved inner tube, and the exhaust inlet and the exhaust outlet extend from the muffler housing.